The frequency of your phone backups broadly depends on how often you add new files to your phone and how important they are.
For example, if you’re constantly taking family photos, or recording important notes, you’ll want to back up your phone quite often just in case the worst happens.
Many people find backing up their phone once a week is more than adequate.
If you’re using your phone for business purposes, and you get work emails or documents to your device, you may find more frequent backups are necessary.
You can also ensure that your backups are timed for convenience, i.e. not in your core working hours or set to complete after a particular project. If you don’t have automatic backups scheduled on your phone, try setting a reminder in your calendar or to do list app to ensure you don’t forget.